Br J Clin Pharmacol. 1993 Sep; 36(3): 237-40.

Impaired absorption of paracetamol in vegetarians.

Prescott LF, Yoovathaworn K, Makarananda K, Saivises R, Sriwatanakul K.

University Department of Clinical Pharmacology, Royal Infirmary, Edinburgh, Scotland.

1. The absorption and disposition of paracetamol was investigated in 10 healthy male Thai vegetarians and 10 similar non-vegetarians following an oral dose of 20 mg kg-1. 2. The absorption rate of paracetamol was significantly impaired in the vegetarians compared with the non-vegetarians as shown by a lower mean Cmax (11.7 +/- 1.4 vs 15.6 +/- 1.6 mg l-1; 95% confidence interval of the difference 2.49 to 5.36), increased tmax (median 1.75, range 0.75 to 3 h compared with 0.75 and 0.25 to 2 h) and an increase in the time for input of 50% of the total amount absorbed (0.54 +/- 0.38 compared with 0.20 +/- 0.10 h; 95% confidence interval of the difference 0.063 to 0.61). 3. A significantly lower total 24 h urinary recovery of paracetamol and metabolites (72.1 +/- 5.4 vs 86.4 +/- 5.4% of the dose; 95% confidence interval of the difference 8.0 to 20.6) indicated a decrease in the extent of absorption in the vegetarians also, although the total AUC values did not differ significantly between the two groups. 4. The plasma paracetamol half-life, partial metabolic clearances and fractional urinary excretion of the glucuronide, sulphate, cysteine and mercapturic acid conjugates of paracetamol were similar in the vegetarians and non-vegetarians.